Osteoporosis, both post-menopausal and senile, is a major health care problem of the elderly, increasing in importance as our population ages. It results from an imbalance has, as a long-term goal, the understanding of the role that osteoblastic protein secretion plays in differentiation, from the standpoint both of secreted, soluble effector molecules, and secreted proteins which help to shape and form the extracellular matrix (ECM). Currently, there is little information on the number of different proteins that are secreted by osteoblasts, their identities and characteristics, and the roles they play in inducing or maintaining osteoblastic phenotype. There is virtually no information concerning the role of the ECM in these same processes. This proposal addresses these areas, using high resolution electrophoretic techniques as well as Northern blot analysis. Specific aims 1 and 2 are to identify and characterize the secreted proteins of human osteoblastic cells in culture and correlate their expression with the expression of known marker proteins such as osteonectin or osteocalcin. Specific aim 3 will examine whether or not bone cells obtained from individuals of different ages express the same proteins, to the same extent. Specific aim 4 will correlate the secreted proteins of bone cells with the proteins found in human bone (Project 5), while specific aim 5 will explore the effects of various soluble effector molecules (e.g., PTH, vitamin D3) on protein secretion in these cells. In the above studies, we will emphasize a new antigen from Saos-2 cells, P80. Specific aims 6-9 will examine the effect of bone ECM on osteoblastic phenotype in several ways. Specific aim 6 will examine in detail a new finding that MG-63 cells alter shape and osteonectin production when grown on type I collagen; under this specific aim we will also explore other purified components of ECM for phenotypic effects. Specific aim 7 will examine natural ECM as a growth substrate for osteoblastic cells, while specific aim 8 asks whether the age of the natural ECM (e.g., age of donor) alters its effects. Finally, in specific aim 9 we will study the relationship between the ECM effects and effects of hormones and vitamins on expression of osteoblastic phenotype.